The overall objective is to explore the surface chemistry of teeth as it relates to caries resistance. It is known that teeth are most susceptible to caries soon after eruption and that a certain caries resistance is acquired gradually, presumably as a result of post-eruptive changes in the surface enamel. Changes in the properties of dental enamel such as permeability, increase in mineral, and increase or change in organic components will be investigated as a function as post-eruptive age. In vitro and new in vivo methods will be employed. The concentrations of trace elements including molybdenum, copper, strontium, zinc and magnesium will be determined in surface enamel, using a new enamel biopsy procedure and new ultramicroanalytical procedure. The trace elements have been related to caries prevalence. Their chemical status in plaque and saliva will also be investigated. Conditions which favor deposition of topical fluoride as apatitic fluoride will be explored, including the use of catalysts, solutions formulated to favor formation of fluorapatite over calcium fluoride, and surface coatings designed to temporarily trap the applied fluoride. A new method for determining the amounts of apatitic fluoride and calcium fluoride will be employed in these studies.